 Wysłany: Śro 22:45, 12 Lis 2008 Temat postu: Permian Triassic extinction event |
|
| The Permian–Triassic (P–Tr) extinction event, informally known as the Great Dying,[1] was an extinction event that occurred 251.4 million years ago,[2][3] forming the boundary between the Permian and Triassic geologic periods. It was the Earth's most severe extinction event, with up to 96 percent of all marine species[4] and 70 percent of terrestrial vertebrate species becoming extinct; it is the only known mass extinction of insects.[5][6] Fifty-seven percent of all families and 83% of all genera were killed. Because so much biodiversity was lost, the recovery of life on earth took significantly longer than after other extinction events.[4] This event has been described as the "mother of all mass extinctions".[7] The pattern of extinction is still disputed,[8] as different studies suggest one[2] to three[9] different pulses. There are several proposed mechanisms for the extinctions; the earlier peak was likely due to gradualistic environmental change, while the latter was probably due to a catastrophic event. Possible mechanisms for the latter include large or multiple bolide impact events, increased volcanism, or sudden release of methane hydrates from the sea floor; gradual changes include sea-level change, anoxia, increasing aridity,[10] and a shift in ocean circulation driven by climate change.
http://en.wikipedia.org/wiki/Permian%E2%80%93Triassic_extinction_event |
|
